Unit 1 Earth Flashcards
Earth’s shape
Oblate spheroid
Equator
The line around the Earth’s widest point as aligned with its rotation, 0 degrees latitude. Divides the northern and southern hemispheres.
Tropics
Two lines around the Earth making marking the furthest north (Cancer, 21st June) and south (Capricorn, 21st December) that the Sun appears at the zenith. 23.5 degrees north and south.
Latitude
Angle of measurement taken from the line of the Equator (0 degrees) down to the South Pole (-90 degrees) and up to the North Pole (+90 degrees). Gives an angle North-South.
Longitude
An angle of measurement taken from a North-South line running through Greenwich, London, UK. Gives an angle East-West.
Pole
Geographic: the places on the Earth’s surface that mark the Earth’s axis of rotation. Magnetic: the places on the Earth’s surface that mark the emergence of it’s magnetic field lines.
Horizon
The furthest visible part of the Earth from an observer’s location (at a perfectly flat place); nothing beyond it can be seen due to the curvature of the Earth.
Meridian
Wherever an observer is, the line that runs from the South to the North across the sky.
Zenith
Wherever an observer is , this is directly up, 90 degrees from the horizon in all directions.
Van Allen Belts
Layers of charged particles surrounding the Earth which are held in place by the magnetic field. These layers of radiation stop high speed electrons harming life on Earth.
Earth’s diameter
13000km
Solar day
24hrs
Earth rotational period
23hrs 56mins
Evidence that the Earth is not flat.
Ships disappear over the horizon.
Satellites orbit the Earth.
Curvature of the Earth’s shadow during a partial lunar eclipse.
Tilt of the polar axis.
66.5 degrees to the plane on which it orbits (the ecliptic).
The Sun resides over latitudes between 23.5 degrees between the equinoxes.
Prime Meridian.
North-south line running through Greenwich, London where longitude is measured from (0 degrees east/west).
Skyglow.
A form of light pollution that hinders our view of the night sky.
Sources of light pollution.
Floodlights.
Street/motorway lights.
Domestic/industrial security lamps.
Lights in car parks/shopping centres etc.
How did Eratosthenes measure the Earth’s circumference?
Eratosthenes was in Alexandria and found that on the 21st June the Sun was not directly overhead. The following year he was in Syene and measured the length of the shadow of a stick. The year later he did the same in Alexandria. Using triganometry and he calculated that Alexandria was 7 degrees further around the Earth than Syene. Eratosthenes estimate the distance from Alexandria to Syene and calculated the circumference by find the distance of 1degree and multiplying it by 360 degrees.
What gases are in the Earth’s atmosphere?
Nitrogen (78%), oxygen (21%), argon (1%), carbon dioxide (0.04%), water vapour (1%) and traces of other gases.
What is 100km above the Earth’s surface?
The Kármán Line (where astronauts generally agree the edge of the atmosphere is).
Benefits of having an atmosphere.
Absorption of harmful UV Ray’s which can cause skin cancer.
Absorption of harmful X-Ray’s and gamma rays.
Regulates the temperature allowing water to exist.
Provides oxygen to breathe.
Partly protects us from meteorites.
What are some of the drawbacks, for astronomers, of the atmosphere?
Refraction of light as it passes through the turbulent air causing stars to twinkle, restricting resolution.
Selective scattering of shorter wavelengths preventing observations during the day.
Absorption and reflection of certain electromagnetic waves from space meaning most Gamma Ray, X-Ray and uv Ray telescope must be in orbit.
What do electrons in the ionosphere do to the longest radio waves?
Reflect them.
How are some of the shorter microwaves absorbed?
They are absorbed by water vapour (H2O) and oxygen (O2).
What gases is most IR radiation absorbed by?
H2O, CO2 and Methane (CH4).
What gases are most UV wavelengths absorbed by?
O3 and O2.
X-rays and gamma rays are absorbed by which gases?
Oxygen and Nitrogen.
Two types of telescope.
Refractor- convex lens collects the light and brings it to a focus.
Reflector-curved mirror collects light.
What is a lens or mirror called?
An objective. It’s size refers to it’s diameter.
Advantages of large telescopes.
They collect more light in proportion to area and have a higher resolution in proportion to diameter.
How many times higher resolution does a 10 metre telescope have over a 2 metre telescope.
Collects 25 times more light so,
25=5^2 so has 5 times as much resolution.
More light entering a telescope means…
smaller objects become visible.
Most modern telescopes are reflectors. Why?
Mirrors can be manufactured with greater precision and are easier to transport.
Ideal observation sites consider…
atmospheric conditions such as cloud cover, air turbulence, sky brightness, water vapour content, access, utilities likelihood of earthquakes and ground stability.
Advantages of using telescopes in orbit.
No atmosphere to blur/reduce resolution of the images.
No light pollution.
No adverse weather problems.
Longer observation periods.
Ability to detect “other” wavelengths such as gamma rays, IR and X-rays.
Disadvantages of using telescopes in orbit.
Reduced lifetime.
Difficult/impossible to repair or upgrade.
More expensive to build and launch into orbit.
What are the Van Allen Belts?
Two doughnut shaped rings, made of high energy particles, that spin above the Earth. The lower belt can be hazardous when astronauts or experiments if exposed to the radiation for a long time. The Inner Belt is made of mainly protons, whereas the outer is made mainly of electrons.
